Dermatomyositis
What is Dermatomyositis?
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Dermatomyositis is an autoimmune connective tissue disorder which affects primarily the skin and the muscles.
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Who gets Dermatomyositis?
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Dermatomyositis typically affects adults. It is twice as common in women.
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It is not a common disease. It is combined with Polymyositis when population studies have been done. There is often an overlap between the 2 conditions. For every 100,000 people only 5-22 have these conditions, with only 2 in every 100,000 being diagnosed with the disease. This means that in a small city of 200,000 only 4 people are diagnosed every year with these conditions, with no more than 44 at any given time having these diseases!
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What are the symptoms of Dermatomyositis?
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Dermatomyositis is an autoimmune condition that results in a very particular skin rash, as well as inflammation and weakness in the muscles. Very rarely, it can cause only the skin rash.
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A typical rash is violaceous and occurs around the eyes, the upper chest, dorsum of the fingers, the outer thighs. There can be areas of more deep pigmentation and lesser pigmentation as well. Sometimes there can be changes in the scalp that look a bit like psoriasis as well.
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There can be patches of a violaceous rash over the extensor surface of joints. These patches can be scaling. There can also be redness of the middle of the face, similar to the butterfly rash of Lupus.
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The hands can look like 'mechanics hands' with fissuring of the sides of the fingers and rough skin.
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If the muscles involved usually there is weakness in the muscles of the thighs and the upper shoulders. usually this comes on over a few months. Muscles can be tender but not in the majority of people.
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How do we diagnose Dermatomyositis?
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The diagnosis is made clinically, on the basis of the nature of the skin rash, and the presence of the muscle weakness. Sometimes, if the rash is not typical, it will be biopsied to confirm a diagnosis.
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Investigations will be done looking for signs of muscle inflammation: CK a muscle enzyme is usually high.
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Specific immune antibodies will be tested for such as ANA, ENA, Jo1.
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Testings will be done looking at the blood, the kidney and liver function and thyroid function.
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Sometimes an MRI may be done of affected muscles if the diagnosis is not clear, particularly if the CK is normal.
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Testings will also be done looking for any sign of malignancy, as Dermatomyositis can also be associated with malignancy, and can even be a precursor to malignancy in some people. Speak with your Rheumatologist more about this who will tailor the investigations for you personally.
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How do we treat Dermatomyositis?
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Dermatomyositis is treated with DMARD therapy. These are drugs that target the immune system in order to stop the immune system attacking its own body. Common drugs that we use are Methotrexate.
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Prednisolone will be given in the short term to control symptoms. Usually this is given as tablets, but sometimes if symptoms are severe, infusions can be given. We try and avoid prednisolone long term in Rheumatology as it has a lot of side effects when given for prolonged periods of time.